Electrical potentiometer



Jan. 8, 1963 s. A. DOUGLAS 3,072,871

I ELECTRICAL POTENTIOMETER Filed July 14, 1961 I 4 Sheets-Sheet 1 1 0064 45 IN VEN TOR.

Jan. 8, 1963 s. A. DOUGLAS 3,072,371

ELECTRICAL POTENTIOMETER Filed July 14, 1961 4 Sheets-Sheet z jiMflA flew/exam;

INVENTOR.

"MZ M Jan. 8, 1963 s. A. DOUGLAS 3,072,871

ELECTRICAL POTENTIOMETER Filed July 14, 1961 4 sheets-sheet 3 INVENTOR.

Jan. 8, 1963 s. A. DOUGLAS ELECTRICAL POTENTIOMETER 4 Sheets-Sheet 4 Filed July 14, 1961 JadL I95 INVENTOR ATTORNEY United States Patent 3,072,871 ELECTRICAL POTENTIOMETER Samuel A. Douglas, Endicott, N.Y., assiguor to General Precision Inn, Link Division, Binghamton, N.Y., a corporation of Delaware Filed July 14, 1961, Ser. No. 124,112 4 Claims. (Cl. 338171) My invention relates to an improved electrical potentiometer or variable resistance, and more particularly, to an improved type of device which readily lends itself to miniaturization without loss of certain desirable features common to larger units. In order to minimize the size and weight of electronic equipment, the reduction of which in turn will lead to additional economies, it is desirable to reduce the size of precision potentiometers as much as possible. While a variety of very small potentiometers presently are available, none of them, to my knowledge, can accommodate a plurality of adjustable taps. A variety of electronic devices, particularly analog computers, require precision potentiometers having a plurality of taps, which, preferably, can be adjusted in the field.

Therefore, it is a primary object of the present invention to provide an improved variable resistor device of the type described.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the features of construction, combinations of elements, and arrangement of parts which will be exemplified in the constructions hereinafter set forth, and the scope of the invention will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention reference should be had to the following detailed description taken in connection with the accompanying drawings, in which:

"FIG. 1 is an exploded cross-section view in perspective, of an exemplary embodiment of the invention.

FIG. 2 is a cross-section view of a partly-assembled potentiometer constructed in accordance with the invention.

FIG. 3 is a rear end view of the invention, with certain portions partly cut away to show the terminal connection space portion of the device.

FIG. 4 is a front end view of the invention, with portions of the potentiometer wiper arm assembly shown cutaway in order to facilitate illustration of the tap mounting arrangement of the invention.

FIG. 5 is a blown-up detailed view of an adjustable tap mounted in the invention, useful in understanding how the taps utilized in the invention may be adjusted.

FIG. 6 is a' view of the adjustable tap made for use with the present invention, together with its attached pigtail, or connection wire.

- Referring principally to FIGS. 1 and 2, the improved potentiometer may be seen to comprise a generally cylindrical core 1 having an inner member 10 and an outer member 12, formed preferably of an insulating molded plastic, such as a phenolic, a melamine, or a diallyl phthalate, for example. Members 10 and 12 may be molded separately and then permanently bonded together with member 10 concentrically installed inside member 12. Inner core member 10 is provided with a plurality of outwardly projecting ribs or fins 16, 16 which extend to the inner surface of outer core member 12, thereby providing a plurality of passageways 3, 3 which extend parallel to the axis of cylindrical core member 1, as best seen in FIG. 4. In molding core 1, it sometimes may be preferred to provide inwardly-projecting ribs as part of outer member 12 in lieu of the outwardly-projecting ribs 16, 16. Bearing means shown as comprising ball bearing assemblies 13 and 19 seated in a central bore through member I carry rotatable shaft 2, to which the bearings are-pressed. On the left end of shaft 2, a rotatable wiper assembly 20 fixedly attached to insulating collar 23 is connected to shaft 2 by means of screw 21, which threads into the end of shaft 2. The wiper assembly, best seen in FIGS. 2 and 4, comprises insulating bushing 23 to which a resilient wiper arm preferably formed of Phosphor bronze or the like, is cemented. Insulating bushing 23, which is formed of Micarta or a fiber or equivalent insulating material, is countersunk to accommodate the head of screw 21, the threaded portion of which screws into the end of shaft 2. An electrical contact tip 25 of conventional precious-metal type is mounted on end 26 of wiper arm 20, and contact tip 25 traverses the potentiometer resistance element 30 as shaft 2 is rotated.

Wiper arm '20 also includes a forwardly-projecting tab 28 which registers with a slot 29 (see FIGS. 1 and 3) in the drive arm 27 of an adjacent potentiometer (not shown) mounted concentrically to be driven with the device shown. It is assumed that the drive arm of the adjacent potentiometer would be identical to resilient drive arm 27 shown connected to rotate shaft 2 in FIG. 2. Cover cylinder 31, shown slightly removed to the left in FIG. 2, is open at each end in instances where plural potentiometers, or other devices to be ganged, are stacked. It will be seen that a further potentiometer (not shown) identical to the device of FIG. 2 could be concentrically mounted with the device of FIG. 2, with the base shoulder 32 of such a. further potentiometer registering with recessed shoulder 33 of cylindrical cover 31. Covers similar to cover 31 but with closed forward ends may be provided for use with potentiometers whose wiper arms end, and connection of slip-ring 38 by wire 40 to a terminal 42 serves to provide the wiper arm voltage as an output from the device.

Resistance element 30 is shown as comprising a conventional insulating strip or card wound with many turns of resistance wire. While contact tip 25 of the wiper arm is shown urged by the spring force of the arm to bear against the edge of the resistance element, it is within the scope of the invention to utilize a modified form of wiper arm which urges its contact tip outwardly against an exposed portion of the inner surface of resistance element 30. The arrangement shown in FIG. 2 is preferred, however, because it leaves more room axially for adjustable taps to be located when the wiper arm contact is arranged, as shown, to traverse the edge, rather than the side, of the resistance element. Also, while a wirewound resistance element is shown in the drawings, it is quite within the scope of the invention to utilize a conductive plastic resistance element, or a film-type resistance element. a

The cylindrical outer surface 48 of outer core member 12 carries ring-like spacer 50 which is formed by any suitable insulating material and which serves to locate resistance element 30 in an axial sense. Quite obviously, spacer ,50 may comprise an integral portion of member 12, if desired. The use of separate spacers, however,

of adjustable taps. If desired the outer surface 54 of resistance element 30 may be taped or painted for the purpose of providing mechanical and/or electrical protection to the winding. The ends of resistance element 30 are connected by wires 61, 61 to terminals 42, 42 located around the base of the potentiometer. A hole 56' (see FIG. 2) through outer core member 12 allows wires 61, 61 to lead from resistance element 30 through a portion of one passageway, to the terminal recess of the potentiometer.

One or more adjustable tap assemblies are provided, each tap assembly 4 comprising a resilient wire 5 having a relaxed shape substantially as shown in FIG. 6, and a flexible wire lead 6 adapted to connect the tap to a potenti-ometer terminal. An adjustable tap may be inserted in any of passageway 3, 3, and when pushed into the position shown in FIG. 2, the contact tip 7 of the tap will be seen to bear against the inner surface 46 of resistance element 30, thereby making electrical contact with the resistance element. Sufiicient resilience is provided in each tap so that it holds itself tightly in position once installed. As seen best in FIGS. 2 and 6, aprotrusion such as loop -8 may be provided at the base end of the tap, to seat against shoulder 65 of the core and insure that vibration or acceleration will not allow the tap to work upwardly to where it might interfere with the rotatable wiper assembly. Because each of passageways 3, 3 is narrower in cross-section on its radially inward side, a tap located in one of the passageways is very unlikely to move. Portion 3a of each tap bears against and nests in the narrow inner corner of the passageway in which the tap is installed. As best seen in FIG. 5, the portion 3a of the tap resting in'the corner-of a passageway will 1 operate as a pivot point as a tap is adjusted withina given passageway to the precise point desired of that are of the" resistance element registering with the given passageway.

In FIG. 5 the tap is shown in dashed lines at two extreme positions of adjustment. -In order to adjust the contact location, the tip 7 of the tap merely need be urged radially inwardly to free it from the resistance elemcnt,-and then the tap may be swung throughout its adjustment range, and upon being released, contact tip'7 again will be urged outwardly by the spring force of the tap. Because the range of adjustment of the contact tip of a tap is capable of overlapping that of a similar tap in anadjacent passageway, there is no turn of resistance wire or no angle of resistance which cannot be reached by an appropriately located tap. It may be noted that it is virtually impossible for one tap to accidentally short to an adjacent tap, in the absence of catastrophic failure. Furthermore, because almost all of each tap is nested in its respective passageway, each tap is protected from being accidentally moved.

The flexible lead 6 of adjustable tap '4 is shown in FIG. 2 soldered at 43 to terminal post 42, which is molded into core member 12. A plurality of similar terminal posts 42, 42 extend through member 12 to facilitate connection of the potentiometer winding, wiper contact and adjustable taps to external circuitry. Circular 'cover' 66, which is bored to accommodate shaft 2., closes the terminal end of the potentiometer. Cover 66 may be held on by a single screw, such as 67, which threads into inner core member 10.

It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are etficiently attained, and since certain changes may be made in the above constructions without departing from the scope of the invention, it is intendedthat all matter contained in the above description or shown "adapted to-se'at within an inner 21 in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

Having described my invention, What I claim as new and desire to secure by Letters Patent is:

l. A variable resistance device, comprising, in combination: a substantially cylindrical core member having a plurality of passageways of substantially triangular crosssection arranged in circular array about the central axis of said core member, each of said passageways having a pair of walls which converge in a direction toward the inner edge of the passageway which they bound to form an inner corner in each passageway; a resistance element mounted on the exterior surface of said core member and arranged to extend beyond one end of said core mem her; a rotatable shaft journalled in said core member; a wiper arm mounted on said shaft and adapted to traverse said resistance element; and a flexed resilient wire tap member lodged in at least one of said passageways, the spring force of said tap member being exerted between said inner corner ofsaid one of said passageways and a selected point on said resistance element.

2. A variable resistance device, comprising, in combination: a substantially cylindrical core member; an

axially-disposed rotatable shaft concentrically journalled in said core member; a plurality of passageways of substantially triangular cross-section spaced around said shaft and extending'through said core member, a resistance element mounted partially on the exterior surface of said cylindrical core member and arranged to extend beyond one end of said core member; a wiper arm adapted to be rotated by said shaft, thereby to traverse an electrical contact along said resistance element; and an adjustable tap comprising a resilientmember adapted to hold itself in. oneOf'saidpassageWays by means of its spring force and adapted to urge a contact tip against the inner surface of said resistance element, said adjustable tap including said contact tip at one end and a central pivot portion corner of said one of said triangular passageways.

3. Apparatus according to claim 2, in which said adjustable tap also includes a protuberance adapted to seat against an axial end of said core member to minimize undesired movement of said tap through said one of said passageways.

4. A variable resistance device, comprising, in combination: a substantially cylindrical core member; an axiallydisposed rotatable shaft concentrically journalled in said core'member; a plurality ofpassageways of substantially triangular cross-section spaced around said shaft and extending through said core member, a resistance element mounted partially on the exterior surface of said cylindrical core member and arranged to extend beyond one 1 References Cited in the file of this patent UNITED STATES PATENTS Takats Nov. 25, 1952 Dion Mar. 1, 1960 

1. A VARIABLE RESISTANCE DEVICE, COMPRISING, IN COMBINATION: A SUBSTANTIALLY CYLINDRICAL CORE MEMBER HAVING A PLURALITY OF PASSAGEWAYS OF SUBSTANTIALLY TRIANGULAR CROSSSECTION ARRANGED IN CIRCULAR ARRAY ABOUT THE CENTRAL AXIS OF SAID CORE MEMBER, EACH OF SAID PASSAGEWAYS HAVING A PAIR OF WALLS WHICH CONVERGE IN A DIRECTION TOWARD THE INNER EDGE OF THE PASSAGEWAY WHICH THEY BOUND TO FORM AN INNER CORNER IN EACH PASSAGEWAY; A RESISTANCE ELEMENT MOUNTED ON THE EXTERIOR SURFACE OF SAID CORE MEMBER AND ARRANGED TO EXTEND BEYOND ONE END OF SAID CORE MEMBER; A ROTATABLE SHAFT JOURNALLED IN SAID CORE MEMBER; A WIPER ARM MOUNTED ON SAID SHAFT AND ADAPTED TO TRAVERSE SAID RESISTANCE ELEMENT; AND A FLEXED RESILIENT WIRE TAP MEMBER LODGED IN AT LEAST ONE OF SAID PASSAGEWAYS, THE SPRING FORCE OF SAID TAP MEMBER BEING EXERTED BETWEEN SAID INNER CORNER OF SAID ONE OF SAID PASSAGEWAYS AND A SELECTED POINT ON SAID RESISTANCE ELEMENT. 